[44.13] Forbidden Spectral Lines from the Solar Corona Below 1000 \AA

William E. Behring (NASA Goddard Space Flight Center)

Visible wavelength spectral lines formed in the solar corona created great
interest when their origin in the forbidden transitions of highly ionized atoms
was first discovered by W. Grotrian and B. Edlen, because that origin implied a
temperature of about one million degrees K for the corona. These lines have
since been discussed by many investigators. Additional forbidden lines in the
1000 to 2000 \AA\ spectral region have since been discussed by Feldman and
Doschek, and other authors. However, not as much attention has been paid to
the forbidden coronal lines in the wavelength region below 1000 \AA, a regime
in which also appear many strong lines which are permitted by the electric
dipole selection rules. Many of these lines, both predicted and observed, have
been reviewed by Kaufman and Sugar (1986). Besides their intrinsic interest,
they may serve in combination with the permitted lines as density diagnostics
when the coronal density is not too high. They may even serve this purpose in
the low density parts of solar flares, if such regions exist.

This paper will discuss in particular some of those lines which may be expected
in the Mg I and Be I sequences, as well as offer a brief discussion of other
isoelectronic sequences which may produce observable forbidden lines at
wavelengths below 1000 \AA.